1. Technical Field of the Invention
This invention relates to radio telecommunication systems and, more particularly, to a system and method of routing emergency service (e.g., 9-1-1) calls from a mobile station to a Public Safety Answering Point (PSAP).
2. Description of Related Art
In existing radio telecommunications networks, there are several methods of routing emergency services calls (for example, 9-1-1 calls) initiated by a mobile subscriber to the appropriate PSAP. The appropriate PSAP may be determined, for example, based on time-of-day and/or geographic considerations. For example, an emergency call from a mobile station traveling on a highway may be routed to different PSAPs, depending on the location of the MS. In addition, some PSAPs may be operational only during certain hours.
FIG. 1 is a message flow diagram illustrating a first existing method of routing emergency calls in deployed cellular networks. When a mobile station 11 originates an emergency call at 12, the serving mobile switching center (MSC) 13 performs an analysis at 14 of the called number and determines that the call is an emergency services call. The serving MSC then determines an approximate location of the mobile station based, for example, on the location of the serving cell or sector. An appropriate PSAP 15 is then selected, based on either location or time-of-day, and a trunk is established to the selected PSAP at 16. However, other factors which could influence the choice of PSAP are not considered, and the PSAP has no advanced warning that the call is coming.
FIG. 2 is a message flow diagram illustrating a second existing method of routing emergency calls in deployed cellular networks. TIA/EIA/PN3581 (J-STD-034), which is hereby incorporated by reference herein, utilizes a selective router node 21 in the cellular network. The selective router 21 may be located outside the serving MSC and is typically located outside of any associated home location register (HLR). When the mobile station 11 originates an emergency call at 22, the serving MSC 13 performs an analysis of the called number at 23, and determines that the call is an emergency services call. The serving MSC then determines an approximate location of the mobile station. A call setup signaling message 24 is then utilized to provide the selective router 21 with routing digits which identify the cell or sector where the calling mobile station 11 is located. In Phase I of J-STD-034 implementation, the granularity of the location information is defined down to the cell or sector level. In Phase 2 of J-STD-034 implementation, the granularity of the location information will be defined down to 125 meters, 65 percent of the time, in both the X and Y directions.
The selective router 21 then identifies the PSAP 15 which corresponds to the identified cell or sector at 25, and a trunk is established to the selected PSAP at 26. However, factors other than location which could influence the choice of PSAP are not considered, and the PSAP has no advanced warning that the call is coming.
In order to overcome the disadvantage of existing solutions, it would be advantageous to have a system and method of routing an emergency services call which provides an intelligent choice of PSAPs, warns the PSAP that an emergency call is coming, and provides the PSAP with advanced information regarding the context of the call.
Although there are no known prior art teachings of a solution to the aforementioned deficiency and shortcoming such as that disclosed herein, U.S. Pat. No. 5,239,570 to Koster et al. (Koster) and U.S. Pat. No. 5,598,460 to Tendler (Tendler) discuss subject matter that bears some relation to matters discussed herein. Koster discloses a 9-1-1 switched access system in which shared lines are made as reliable as dedicated lines. Thus, Koster does not teach or suggest a method of routing an emergency services call which provides an intelligent choice of PSAPs, warns the PSAP that an emergency call is coming, and provides the PSAP with advanced information regarding the context of the call.
Tendler discloses a system for enhancing the reliability of rescue services by providing a 9-1-1 back-up system in which the termination of an emergency call is sensed, followed by dialing the telephone number of a predetermined dispatch office. The dispatch office then calls back the nearest PSAP to ascertain whether or not rescue personnel are on their way. Thus, Tendler does not teach or suggest a method of routing an emergency services call which provides an intelligent choice of PSAPs, warns the PSAP that an emergency call is coming, and provides the PSAP with advanced information regarding the context of the call.
Review of each of the foregoing references reveals no disclosure or suggestion of a system or method such as that described and claimed herein.